A macromolecule is a large, complex molecule typically composed of thousands of atoms. Macromolecules are vital to biological processes and include four primary categories: proteins, nucleic acids, carbohydrates, and lipids. Proteins, made of amino acids, play roles in structure, enzymes, and signaling. Nucleic acids, such as DNA and RNA, store and transmit genetic information. Carbohydrates serve as energy sources and structural components, while lipids function in energy storage, membrane formation, and signaling. Understanding macromolecules is essential for comprehending cellular functions and biological systems.